Camera objective of variable focal length

ABSTRACT

A pancratic camera objective of varifocal ratio close to 5:1, and with a relative aperture varying between 1:1.2 in a wide-angle position and 1:1.5 in a telephoto position, has a pair of axially shiftable negative components bracketed by a pair of substantially fixed positive components. Its negative third component is more widely separated from its positive fourth component in the wide-angle position than in the telephoto position.

FIELD OF THE INVENTION

My present invention relates to a pancratic camera objective of the general type described in commonly owned U.S. Pat. No. 4,087,160, including a varifocal forward lens group and a fixed-focus rear lens group centered on a common optical axis, the forward lens group consisting of a substantially axially fixed positive first component, axially shiftable negative second and third components, and an axially fixed fourth component. The first three components form a lens assembly of dispersive character; the third component approaches the fourth component more closely in a telephoto position of maximum overall focal length f_(max) than in a wide-angle position of minimum focal length f_(min) while having an inversion point at an intermediate position of overall focal length f_(med).

BACKGROUND OF THE INVENTION

The prior patent referred to above discloses two specific embodiments, one of them with a varifocal ratio f_(max) /f_(min) approximately equal to 8, the other with a varifocal ratio of about 10. In the wide-angle position of the objective, its relative aperture is 1:1.2 according to the first embodiment and 1:1.8 according to the second one; the first system, accordingly, falls in the so-called XL (=existing light) class permitting--in a cinematographic camera--the taking of indoor motion pictures without additional illumination. The effective area of the third (negative) component of an objective as described in that patent is restricted to provide full illumination of the fourth (positive) component by axially incident light rays in the wide-angle position but less than full illumination in the telephoto position, thereby enabling a reduction in the lens diameters of the front component.

OBJECT OF THE INVENTION

The object of my present invention is to provide an objective of the general type described above which is of simpler construction, does not necessarily require a restriction of the effective area of the third component and has a relative aperture similar to that of the first embodiment disclosed in the prior patent, i.e. about 1:1.2 in the wide-angle position, while still affording a large varifocal ratio of approximately 5:1.

SUMMARY OF THE INVENTION

I realize this object, pursuant to my present invention, with a pancratic objective of only seven lens members (one of them a doublet) in its varifocal forward group, i.e. with a first component consisting of three singlets, having parameters substantially as given hereinafter.

BRIEF DESCRIPTION OF THE DRAWING

My invention will now be described in detail with reference to the accompanying drawing the sole FIGURE of which diagrammatically illustrates my improved pancratic objective.

SPECIFIC DESCRIPTION

In the drawing I have shown the wide-angle position of a pancratic objective according to my invention, including a varifocal forward lens group with components 1-4 and a rear lens group 5. The substantially stationary positive component 1 (which may be limitedly shiftable for focusing purposes) comprises a front lens in the form of a negative meniscus L₁ with radii r₁, r₂ and thickness d₁, two positive lenses L₂ (radii r₃, r₄ and thickness d₂) and L₃ (radii r₅, r₆ and thickness d₃) which intervening air spaces s₁ and s₂. A variable air space s₃ separates lens L₃ from the axially shiftable component 2 consisting of a singlet L₄ in the form of a negative meniscus (radii r₇, r₈ and thickness d₄) separated by an air space s₄ from a doublet consisting of lenses L₅ (radii r₉, r₁₀ and thickness d₅) and L₆ (radii r₁₀ , r₁₁ and thickness d₆). Another variable air space s₅ lies between component 2 and component 3 which consists of a single lens L₇ in the form of a negative meniscus with radii r₁₂, r₁₃ and thickness d₇. A third variable air space s₆ lies between component 3 and axially fixed component 4 which in this instance consists of two air-spaced biconvex lenses L₈ (radii r₁₄, r₁₅ and thickness d₈) and L₉ (radii r₁₆, r₁₇ and thickness d₉), the intervening air space having been designated s₇. The light path between components 3 and 4 is restricted by a mounting 6 for lens L₇, acting as an ancillary diaphragm.

A reflex prism P of thickness d_(p), whose planar faces have been designated r_(p) ' and r_(p) ", is separated by an air space s₈ from lens L₉ and by a diaphragm space s_(d) '+s_(d) " from component 5, the latter space containing an iris diaphragm 7. Component 5 consists of five air-spaced singlets, namely a biconvex lens L₁₀ (radii r₁₈, r₁₉ and thickness d₁₀), a positive meniscus L₁₁ (radii r₂₀, r₂₁ and thickness d₁₁), a biconcave lens L₁₂ (radii r₂₂, r₂₃ and thickness d₁₂), a planoconvex lens L₁₃ (radii r₂₄, r₂₅ and thickness d₁₃) and another positive meniscus L₁₄ (radii r₂₆, r₂₇ and thickness d₁₄); the intervening air spaces have been designated s₉, s₁₀, s₁₁ and s₁₂. The image plane of the objective has been shown at 8.

In the following table I have given representative numerical values for the parameters r₁ -r₂₇, d₁ -d₁₄ and s₁ -s₁₂ of the illustrated optical system, based upon a mean overall focal length f_(med) =1 in the extreme left-hand position of component 3. The table also gives the refractive indices n_(d) and the Abbe numbers ν_(d) of the various lenses.

    ______________________________________                                                            Thicknesses and                                             Lens   Radii       Separations     n.sub.d                                                                             ν.sub.d                             ______________________________________                                                    r.sub.1 = + 6.626                                                   L.sub.1                d.sub.1 = 0.139   1.805                                                                               25.4                                        r.sub.2 = + 2.734                                                                          s.sub.1 = 0.077                                                    r.sub.3 = + 2.734                                                   L.sub.2                d.sub.2 = 0.499   1.620                                                                               60.3                                        r.sub.4 = - 21.705                                                                         s.sub.2 = 0.008                                                    r.sub.5 = + 2.806                                                   L.sub.3                d.sub.3 = 0.333   1.667                                                                               48.4                                        r.sub.6 = + 18.186                                                                                   0.063 f.sub.min                                                      s.sub.3 = 0.635 f.sub.med                                                                1.635 f.sub.max                                          r.sub.7 = + 6.973                                                   L.sub.4                d.sub. 4 =                                                                               0.077   1.713                                                                               53.8                                        r.sub.8 = + 1.143                                                                          s.sub.4 = 0.317                                                    r.sub.9 = - 1.817                                                   L.sub.5    d.sub.5 =         0.077                                                                              1.620   60.3                                             r.sub.10 = + 1.817                                                  L.sub.6                d.sub.6 = 0.213   1.805                                                                               25.4                                        r.sub.11 = ∞                                                                                   1.529 f.sub.min                                                      s.sub.5 = 0.929 f.sub.med                                                                0.278 f.sub.max                                          r.sub.12 = - 1.237                                                  L.sub.7                d.sub.7 = 0.077   1.744                                                                               44.8                                        r.sub.13 = - 4.629                                                                                   0.501 f.sub.min                                                      s.sub.6 = 0.529 f.sub.med                                                                0.180 f.sub.max                                          r.sub.14 = + 6.802                                                  L.sub.8                d.sub.8 = 0.213   1.620                                                                               60.3                                        r.sub.15 = - 2.883                                                                         s.sub.7 = 0.008                                                    r.sub.16 = + 4.703                                                  L.sub.9                d.sub.9 = 0.170   1.620                                                                               60.3                                        r.sub.17 = - 7.120                                                                         s.sub.8 = 0.077                                                    r.sub.p ' = ∞                                                 P                      d.sub.p = 0.387   1.517                                                                               64.2                                        r.sub.p " = ∞                                                              s.sub.d ' + s.sub.d " = 0.116 + 0.139                                        r.sub.18 = + 2.294                                                  L.sub.10               d.sub.10 =                                                                               0.224   1.620                                                                               60.3                                        r.sub.19 = - 7.306                                                                         s.sub.9 ;32                                                                              0.008                                                    r.sub.20 = + 1.225                                                  L.sub.11               d.sub.11 =                                                                               0.221   1.620                                                                               60.3                                        r.sub.21 = + 2.660                                                                         s.sub.10 =                                                                               0.310                                                    r.sub.22 = + 1.290                                                  L.sub.12               d.sub.12 =                                                                               0.166   1.847                                                                               23.8                                        r.sub.23 = + 1.290                                                                         s.sub.11 =                                                                               0.252                                                    r.sub.24 = - 70.722                                                 L.sub.13               d.sub.13 =                                                                               0.255   1.713                                                                               53.8                                        r.sub.25 = - 0.947                                                                         s.sub.12 =                                                                               0.008                                                    r.sub.26 = + 1.137                                                  L.sub.14               d.sub.14 =                                                                               0.174   1.620                                                                               60.3                                        r.sub.27 = + 4.420                                                  ______________________________________                                    

The objective conforming to the foregoing table has a minimum focal length f_(min) =0.666, a median focal length f_(med) =1 and a maximum focal length f_(max) =2.863. Its relative aperture is 1:1.2 in the illustrated wide-angle position and 1:1.5 in the telephoto position at the opposite end of its varifocal range. 

I claim:
 1. In a camera objective of variable focal length including a varifocal foward lens group and a fixed-focus rear lens group centered on a common optical axis, said forward lens group consisting of a substantially axially fixed positive first component, an axially shiftable negative second component, an axially shiftable negative third component and an axially fixed fourth component, said second and third components being displaceable between a wide-angle position of minimum overall focal length and a telephoto position of maximum overall focal length with maintenance of an invarient image plane behind said rear lens group, said third component approaching said fourth component more closely in said telephoto position than in said wide-angle position, the combination of said first, second and third components being of dispersive character,the improvement wherein said first component consists of lenses L₁, L₂ and L₃, said second component consists of lenses L₄, L₅ and L₆, said third component consists of a lens L₇ and said fourth component consists of lenses L₈ and L₉, said lenses having radii of curvature r₁ -r₁₇, axial thicknesses d₁ -d₉ and axial spacings s₁ -s₇ whose numerical values, based on a numerical value of unity for an intermediate overall focal length, together with their refractive indices n_(d) and Abbe numbers ν_(d) are substantially as given in the following table:

    ______________________________________                                                                n.sub.d                                                                              ν.sub.d                                        ______________________________________                                                   r.sub.1 = +6.6                                                       L.sub.1              d.sub.1 =                                                                               0.14     1.81  25                                          r.sub.2 = + 2.7                                                                           s.sub.1 =                                                                               0.08                                                       r.sub.3 = + 2.7                                                      L.sub.2              d.sub.2 =                                                                               0.50     1.62  60                                          r.sub.4 = - 21.7                                                                          s.sub.2 =                                                                               0.01                                                       r.sub.5 = + 2.8                                                      L.sub.3              d.sub.3 =                                                                               0.33     1.67  48                                          r.sub.6 = + 18.2                                                                                   0.06 f.sub.min                                                        s.sub.3 =                                                                               0.64 f.sub.med                                                                 1.64 f.sub.max                                             r.sub.7 = + 7.0                                                      L.sub.4              d.sub.4 =                                                                               0.08     1.71  54                                          r.sub.8 = + 1.1                                                                           s.sub.4 =                                                                               0.32                                                       r.sub.9 = - 1.8                                                      L.sub.5              d.sub.5 =                                                                               0.08     1.62  60                                          r.sub.10 = + 1.8                                                     L.sub.6              d.sub.6 =                                                                               0.21     1.81  25                                          r.sub.11 = ∞                                                                                 1.53 f.sub.min                                                        s.sub.5 =                                                                               0.93 f.sub.med                                                                 0.28 f.sub.max                                             r.sub.12 = - 1.2                                                     L.sub.7              d.sub.7 =                                                                               0.08     1.74  45                                          r.sub.13 = - 4.6                                                                                   0.50 f.sub.min                                                        s.sub.6 =                                                                               0.53 f.sub.med                                                                 0.18 f.sub.max                                             r.sub.14 = + 6.8                                                     L.sub.8              d.sub.8 =                                                                               0.21     1.62  60                                          r.sub.15 = - 2.9                                                                          s.sub.7 =                                                                               0.01                                                       r.sub.16 = + 4.7                                                     L.sub.9              d.sub.9 =                                                                               0.17     1.62  60                                          r.sub.17 = - 7.1                                                     ______________________________________                                    


2. The improvement defined in claim 1 wherein said rear lens group consists of lenses L₁₀, L₁₁, L₁₂, L₁₃ and L₁₄ whose radii of curvature r₁₈ -r₂₇, axial thicknesses d₁₀ -d₁₄, axial spacings s₉ -s₁₂, refractive indices n_(d) and Abbe numbers ν_(d) are substantially as given in the following table:

    ______________________________________                                                              n.sub.d                                                                               ν.sub.d                                         ______________________________________                                                      r.sub.18 = + 2.3                                                  L.sub.10                 d.sub.10 = 0.22                                                                        1.62   60                                                  r.sub.19 = - 7.3                                                                           s.sub.9 = 0.01                                                     r.sub.20 = + 1.2                                                  L.sub.11                 d.sub.11 ` 0.22                                                                        1.60   60                                                  r.sub.21 = + 2.7                                                                           s.sub.10 = 0.31                                                    r.sub.22 = + 1.3                                                  L.sub.12                 d.sub.12 = 0.17                                                                        1.85   24                                                  r.sub.23 = + 1.3                                                                           s.sub.11 = 0.25                                                    r.sub.24 = + 70.7                                                 L.sub.13                 d.sub.13 = 0.26                                                                        1.71   54                                                  r.sub.25 = - 0.9                                                                           s.sub.12 = 0.01                                                    r.sub.26 = + 1.1                                                  L.sub.14                 d.sub.14 = 0.17                                                                        1.62   60                                                  r.sub.27 l = + 4.4                                                ______________________________________                                     